JEE Main 2026 — Physics Electromagnetism

2026mcqmedium

Three identical coils $C_{1}, C_{2}$ and $C_{3}$ are closely placed such that they share a common axis. $C_{2}$ is exactly midway. $C_{1}$ carries current $I$ in anti-clockwise direction while $C_{3}$ carries current $I$ in clockwise direction. An induced current flows through $C_{2}$ will be in clockwise direction when

Official previous-year question

Held on 22 Jan 2026 · Verified 6 Jul 2026.

Options

A
$C_{1}$ moves away from $C_{2}$ and $C_{3}$ moves towards $C_{2}$
B
$C_{1}$ and $C_{3}$ move with equal speeds away from $C_{2}$
C
$C_{1}$ moves towards $C_{2}$ and $C_{3}$ moves away from $C_{2}$
D
$C_{1}$ and $C_{3}$ move with equal speeds towards $C_{2}$

Did you get this right?

Solution

Let the common axis be the z-axis.

$C_1$ is at $z = -d$ , $C_2$ is at $z = 0$ , and $C_3$ is at $z = +d$ .

Current in $C_1$ is anti-clockwise (ACW), producing a magnetic field $B_1$ in the $+z$ direction at $C_2$ .

Current in $C_3$ is clockwise (CW), producing a magnetic field $B_3$ in the $-z$ direction at $C_2$ .

The net magnetic field at $C_2$ is $B_{net} = B_1 - B_3$ . Since $C_1$ and $C_3$ are equidistant and carry equal current, initially $B_{net} = 0$ .

To induce a clockwise current in $C_2$ , Lenz's law states that the induced current must oppose the change in flux. A clockwise induced current produces a magnetic field in the $-z$ direction.

This happens if there is an increasing flux in the $+z$ direction or a decreasing flux in the $-z$ direction.

Case 1: $C_1$ moves towards $C_2$ . The distance decreases, so $B_1$ (in $+z$ direction) increases. This causes an increasing flux in the $+z$ direction.

Case 2: $C_3$ moves away from $C_2$ . The distance increases, so $B_3$ (in $-z$ direction) decreases. This causes a decreasing flux in the $-z$ direction.

Both actions (moving $C_1$ towards $C_2$ and moving $C_3$ away from $C_2$ ) result in a net change in flux that induces a clockwise current in $C_2$ to oppose the change.

Therefore, option (3) is correct.

Your note

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Options

$C_{1}$ moves away from $C_{2}$ and $C_{3}$ moves towards $C_{2}$

$C_{1}$ and $C_{3}$ move with equal speeds away from $C_{2}$

$C_{1}$ moves towards $C_{2}$ and $C_{3}$ moves away from $C_{2}$

$C_{1}$ and $C_{3}$ move with equal speeds towards $C_{2}$